1. Field of the Invention
The present invention relates to a balloon catheter used for intra-aortic balloon pumping (IABP technique) for treatment of acute cardiac insufficiency etc.
2. Description of the Related Art
In the IABP technique, cardiac insufficiency and other deterioration of cardiac functions are treated by inserting into the aorta a balloon catheter comprised of a balloon portion and catheter tube made of a synthetic polymer material and introducing or releasing a shuttle gas into or from the balloon portion through the catheter tube by a driving console so as to make the balloon portion expand and contract in timing with the heart beating and thereby assist the heart beatings.
As the balloon catheter used for the IABP technique, there are known the balloon catheters disclosed in Japanese Unexamined Patent Publication (Kokai) No. 63-206255 and Japanese Unexamined Patent Publication (Kokai) No. 62-114565. In these balloon catheters, it is necessary to detect the heart beating of the patient in order to make the balloon portion expand and contract in timing with the heart beating. As a means for detecting the heart beating of a patient, there is the means of attaching electrodes to the surface of the patient's body or in his or her body and detecting the heart beating as an electrical signal.
Further, as a means for detecting the heart beating from the blood pressure of the patient using the balloon catheter, there is the method of detecting the heart beating by providing the front tip portion of the balloon portion with a blood port, inserting an inner tube communicated with the blood port inside the balloon portion and the catheter tube in the axial direction of the same, and measuring the fluctuation in the blood pressure from a blood pressure outlet.
In such a type of balloon catheter, a bifurcation is connected to the proximal end of the catheter tube outside the body. At this bifurcation there are formed a shuttle gas port for introducing or releasing the shuttle gas into or from the catheter tube and the balloon portion and a blood pressure measurement port communicated to the inside of the inner tube. The shuttle gas port is connected to a driving console. This driving console is used to introduce or release the fluid pressure into or from the balloon portion.
In a balloon catheter of such a construction, there were the following problems. That is, since the catheter tube 24 is inserted into the arterial blood vessel of the patient, considering the discomfort of the patient, the catheter tube is preferably made as small as possible in outer diameter. If the outer diameter of the catheter tube is made small, however, the fluid pressure passage formed inside it becomes smaller, the channel resistance rises, and the timing response of the expansion and contraction of the balloon portion driven by the shuttle gas becomes poorer, making it impossible in some cases to effectively achieve a heart assisting action. The period of the expansion and contraction of the balloon portion is 0.6 second assuming a heart beating of 100 beats/minute. The shuttle gas reciprocates in the catheter tube in a time shorter than this period, so the smaller the channel resistance the better.
Therefore, in the past, the outer diameter of the catheter tube was set as large as possible within the range not significantly increasing the discomfort of the patient, and the timing response of the expansion and contraction of the balloon portion was sacrificed to a certain extent. In the conventional balloon catheter, further, since the inner tube could freely move in the radial direction in the catheter tube, when inserting the catheter tube into the arterial blood vessel of the patient by snaking it along the blood vessel, the inner tube would lay irregularly snaked inside the catheter tube. As a result, when the shuttle gas for making the balloon portion expand or contract passed through the clearance between the outer wall of the inner tube and the inner wall of the catheter tube, an eddy flow was produced, the energy loss of the fluid was increased, the efficiency of the driving console was reduced, and the timing response of expansion and contraction could be worse.
Further, the inner tube would flex due to the catheter tube having to be snaked through the twisted portions of the blood vessel in the body and thereby would block the area around where the shuttle gas port intersects with the extension of the catheter tube, thereby possibly causing a large fluid resistance.